The present invention relates to scale model aircraft particularly, remotely controlled, flying scale models of jet propelled aircraft. In the scale model aircraft industry great efforts are taken to accurately reproduce the particular full scale operational aircraft both in appearance and operational characteristics. Although great strides have been achieved in the industry, one area affecting both appearance and scale model performance has been neglected; that being the jet exhaust nozzle. Operational jet aircraft of the present day are commonly equipped with engine exhaust nozzles having a variable area geometry; that is to say that the exit diameter of the jet exhaust nozzle may be varied depending upon the particular flight regime within which the aircraft is being operated.
Two particular flight regimes that require different exhaust nozzle configurations, for both full scale and model aircraft, are take-off and in flight cruse. Full scale operational aircraft employ maximum exhaust nozzle diameters for take-off and decrease or restrict the exhaust nozzle diameter during in flight cruse. It is an established fact that jet propelled aircraft, full scale or model aircraft, cannot have a cruising velocity, or air speed, greater than the exit velocity of the jet engine exhaust at the tail pipe exhaust nozzle. It is also established that the optimum exhaust nozzle configuration to produce maximum thrust at take-off (requiring a large diameter nozzle opening) is not optimum at cruse where less than take-off thrust is required to propel the aircraft at a constant velocity or air speed. Therefore, full scale operational aircraft are equipped with variable area exhaust nozzles whereby the diameter of the nozzle may be decreased or restricted to a smaller, more optimum, diameter for in flight cruse.
Scale model jet aircraft using ducted fan technology to obtain a propelling thrust from the exhaust nozzle, experience similar nozzle configuration problems as their full scale counterparts; that being that a large diameter exhaust nozzle configuration is desired for take-off however, a smaller or reduced diameter exhaust nozzle diameter is desired for in flight cruse.
Heretofore, scale model jet aircraft, employing a ducted fan propulsion system, have used an "optimum" fixed, non variable, nozzle configuration that although providing nominal performance in both the take-off and in flight cruse regimes, does not provide for maximum performance in either operational regime.